Results from AP Exams

Jiang Yu, Chief Reader

I attended this session to gain some insights into how the AP Physics B exam is scored and what common mistakes students made on the exam.

• Question B1
  • 6.6/10
  • common errors
    • omit one of the three forces or add a normal force on FBD
    • use unconventional labels for their forces
    • units! students often omitted units
    • not recognize buoyancy is measured in Newtons
    • forces that appeared on the FBD often did not match the ones appeared in subsequent calculations
    • not using physics but general language in justification
• Question B2
  • 6.0/15
  • common errors
    • applied kinematic equations for constantly accelerated motion to a motion of changing acceleration
    • not recognize that W=Fd can only be used when F is constant
    • not knowing that spring force is not a constant force
    • explanations are not concise and clear
• Question B3
  • 3.6/10
  • common errors
    • non-linear scaling of axes in graphing
    • best-fit line often is drawn by just connecting points
    • not showing work for calculating slope of the best-fit line
    • not understanding that the light must pass from a higher index of refraction to a lower index of refraction in order to have total internal reflection
• Question B4
  • 3.6/10
  • common errors
    • not reading the question carefully and not answering what is asked
    • not showing enough work beginning with the correct equations and then all the needed steps leading to an answer
    • messing up the horizontal and the vertical dimensions in calculations
    • deficiency in understanding the conservation of momentum
    • using “energy,” “force,” “momentum” and “velocity” interchangeable in explanations
• Question B5
  • 3.6/10
  • common errors
    • misunderstanding of the sign conventions in evolved for heat, work and energy
    • not clear with their justifications, but often simply restated the question, and answer without providing further support
    • connected heat or average kinetic energy to temperature, but not to the internal energy
    • used W = -PΔV and did not discuss the effect of temperature on the pressure
• Question 6
  • 3.5/15
  • common errors
    • simple calculations errors were everywhere
    • incorrect use or value of the magnetic permeability, μo, in Ampere’s Law
    • not understanding the intent of parts (a) & (b)
    • did not clearly understand the nature of the question and the connection of the parts to each other
• Question 7
  • 2.7/10
  • common errors
    • the most common errors were the result of a lack of understanding of atomic states and associated energy levels. Students seemed to choose and use the equations without basic understanding of the physics involved.